With the development of science and technology, flat panel display devices have replaced bulky cathode ray tube (CRT) display devices and increasingly penetrated into people's daily life, and liquid crystal display devices (LCDs) are a kind of flat panel display devices. The main constituent component of a liquid crystal display device is a liquid crystal panel, which mainly includes a color film substrate and an array substrate with liquid crystals filled therebetween. In the array substrate or the color film substrate, there are further provided electrodes, which are useful for generating electric fields and by which, distribution of the electric fields is determined, and the distribution of the electric fields determines deflection of liquid crystals, and thus affects display of the liquid crystal panel. Each of pixel points in the liquid crystal display device has a pixel electrode and a common electrode opposed to it that are provided therein. In the course of imaging, the pixel electrode is controlled by a thin film transistor (briefly called as TFT) and a storage capacitance (briefly referred to as Cs hereinafter, and also referred to as a pixel capacitance) that are integrated in the array substrate to implement an active driving, so that the image display is realized. The thin film transistor, functioning as a switch in control of a voltage supplied to the pixel electrode, is a key for realizing display of the LCD display device, and is directly related to the development direction of flat panel display devices with high performance.
With the development of display technology, and meanwhile for the sake of meeting people's demands for high brightness, high contrast, and low energy consumption, the ADvanced Super Dimension Switch (briefly called as ADS, and also called as ADSDS) technology emerges as the times require. In the prior art, an ADS type array substrate generally includes a pixel electrode and a common electrode located on the same side of a liquid crystal cell, and a multi-dimensional electric field produced between the pixel electrode and the common electrode allows every liquid crystal molecule within the liquid crystal cell to be deflected. Thus, the work efficiency of liquid crystals is enhanced and the viewing angle is increased. Liquid crystal display devices that employ the ADvanced Super Dimension Switch technology have the merits of high aperture ratio of pixel, wide viewing angle, high brightness, low energy consumption, etc.
As the improvement of the ADS technology, high transmittance I-ADS technology, high aperture ADS (briefly called as H-ADS), high resolution S-ADS technology and so on emerge currently. In general, the pixel electrode and the common electrode in the array substrate may include the following two structures. The first structure is that, in a sub-pixel area, the electrode in a lower level is a plate-like common electrode, and the electrode in an upper level is a slit-like pixel electrode; and the second structure is that, in a sub-pixel area, the electrode in a lower level is a plate-like pixel electrode, and the electrode in an upper level is a slit-like common electrode. As illustrated in FIG. 1A and FIG. 1B, a common electrode 20 has a slit-like structure, a pixel electrode is a plate-like electrode. Moreover, the thickness of the common electrode 20 is fixed, and conductivity of the common electrode 20 is smaller so that its power supply ability is weak.
As the provider of a common reference voltage, the principle function of the common electrode lies in that it can maintain a stable reference point for common voltage. Yet, because of special properties of liquid crystals, alternating current drive modes, such as frame inversion, row inversion, column inversion, dot inversion and other mode are usually adopted in liquid crystal display devices. Owing to the presence of Cs and other parasitic capacitance, in an AC drive mode, an AC signal will bring an effect on the common voltage so that it is pulled up or down periodically. If conductive properties of the common electrode are not good, it will affect the display quality of picture of the display device. For example, the display of an image is also accompanied by Greenish, Flick, Crosstalk and other phenomenon.
In order to ensure that a TFT in a sub-pixel area works stably, it is necessary for charges stored on the Cs to maintain the drive voltage of the TFT continually, so that liquid crystal molecules are kept in a stable operating state in a frame period. Accordingly, how to ensure the stability of a voltage across the common electrode in the array substrate, to raise the power supply capability of the common electrode, and to improve the quality of display pictures, become urgent problems that need solving in the industry at present.